1. Field of the Invention
This invention relates to electrical safety provisions in small appliances. More particularly, the invention relates to apparatus for sensing water in hair dryers and for opening both power lines substantially simultaneously.
2. Description of the Prior Art
Hand held hair dryers and similar small electrical appliances are often used in environments creating some risk that the appliances will come into contact with water, thereby creating the danger of electrocution or serious shock to the user. These dangers exist whether or not the power switch of the appliance is on or off because of the presence of electrical potential on conductive parts within the appliance. The use of a double-throw waterproof switch eliminates these dangers when the appliance is turned off, but serves no salutary purpose when power is on.
Ground fault circuit interrupters are often used as safety circuits to limit the danger of a user suffering electrocution or serious shock which may be caused by touching an appliance having an electrical potential. These devices open the power line upon the occurrence of a flow of electrical current to ground through other than the normal return path of the circuit in which the appliance is connected. Since ground fault circuit interrupters require a differential of current flow they are not totally effective shock hazard protectors because there may be situations where a danger of electrocution exists with no such differential. Furthermore, ground fault circuit interrupters are generally large and costly and, therefore, difficult to install into small appliances. Their ability to be reset also makes them unsuitable for small appliances since the user may reset them prematurely. Often they are installed in the walls of newly constructed dwellings so as to automatically protect the user when an appliance is plugged in. However, for older residences there is no such safety feature unless it is installed in or retrofit into the small appliance.
It is also known in the prior art to provide ground fault circuit interrupters for interrupting both the hot and neutral lines simultaneously whenever a fault is present, since it is not known which of the conductors is electrically connected to the hot side of the power line. However, such prior art devices as are capable of relatively quickly opening both lines simultaneously are costly so as to make their use in small appliances prohibitive. Less expensive prior art devices are relatively slow in opening both lines simultaneously and do not, therefore, provide a satisfactory safety feature.
Some prior art shock hazard protectors are known which shut power off when the appliance comes in contact with water. These devices generally have two main features; a sensor means to sense the danger causing condition and an actuator means to rapidly open the power lines. U.S. Pat. No. 4,464,582, for example, shows an automatic power shut off circuit which utilizes a pair of flexible metallic conductors spaced apart a predetermined distance and secured to an electrical appliance in a labyrinthine pattern. When water bridges the space, the circuit energizes a solenoid to open a pair of switches in the power lines to the appliance. Both the sensing and actuation portions of this device are too costly and complex to be incorporated in relatively low cost electrical appliances.
Another type of shock hazard protector is shown in German patent application No. 32 08 147 A1. The sensor part of the device shown in that application is a two-wire circuit arranged at the edges of openings and joints through which water can penetrate. The device also includes a triac having a firing circuit responsive to the sensor. The actuator part of the device is a self-opening mechanical switch which is normally held closed by a fusible wire which is melted upon the firing of the triac. The actuator part of this device is complex and appears relatively costly to assemble for use in a small appliance. The sensor part of this device requires several circuit components and must be triggered by a water bridge across the two-wire circuit. The sensor is, therefore, also relatively costly. The sensor circuit is also admittedly deficient since it is inoperative during the first 1.5 power line half cycles because of the need to charge a capacitor in the firing circuit. This delay plus the risk that some of the electrical components may fail, are unacceptable deficiencies. This German application shows an alternative embodiment which does not have the delay disadvantage but, since it includes several electrical components, there is still a risk of failure.
The complexity of the aforementioned patents results because the devices are intended to turn power off to the small appliance when water bridges a pair of sensor wires, before it touches any high voltage parts of the appliance. The sensor circuit must, therefore, necessarily have a high impedance to insulate the user from shock in the event he or she actually touches the sensor wires. The circuit must also be capable of determining when the wires are bridged and actuating the mechanism which actually opens the power lines. The complexity and high cost of these devices inhibits their use in small appliances.
Accordingly, there is a need for a safe shock hazard protector which is sufficiently inexpensive so it may be included in relatively low cost appliances such as hair dryers, curling irons and the like
It is a further object to produce a low cost shock hazard protector capable of opening both sides of a two-line power source simultaneously.
It is yet another object to produce a hair dryer having a shock hazard protector which is non-resettable.